Justification:
This species is listed as Endangered because self-sustaining populations have an area of occupancy of less than 500 sq km and are represented by only two locations, and because the number of mature individuals has declined over the past three generations.

This species is native to northern California and southern Oregon. Historical range included the Upper Klamath Lake and its tributaries; the Lost River watershed, including Clear Lake Reservoir and upstream into Willow and Boles creeks; Tule Lake; Lower Klamath Lake; and Sheepy Lake. Present distribution includes Upper Klamath Lake and its tributaries, Clear Lake Reservoir and its tributaries, Tule Lake sumps (a small nonreproducing population; Moyle 2002, Scoppettone et al. 1995, USFWS 2007), the Lost River up to Anderson-Rose Dam, and (as a result of recent colonization) the Klamath River downstream to Copco Reservoir and probably Iron Gate Reservoir (USFWS 1994, Moyle 2002). The species is extirpated in Lower Klamath Lake and Sheepy Lake (Moyle 2002), and the populations other than those in Upper Klamath Lake and Clear Lake are not believed to be self-sustaining (NRC 2004).

This species is represented by only two populations that are sustaining themselves without the input of larvae or older suckers from other areas (USFWS 2007).

Total adult population size is unknown. Moyle (2002) informally suggested that population size may be a few thousand, and others have suggested that the adult populations of Upper Klamath Lake and Clear Lake number in the tens of thousands (see USFWS 2007). However, at the present time, it is not feasible to produce a reliable estimate of population size for the Lost River Sucker (USFWS 2007). An apparently nonreproducing population in the Tule Lake sumps includes a few hundred adults (Scoppettone et al. 1995).

Historically, Lost River Suckers were abundant enough to provide an important food resource for indigenous people and later settlers and their livestock (hogs). Now the species is extirpated in Lower Klamath Lake and Sheepy Lake, uncommon in Upper Klamath Lake and Tule Lake, and common only in Clear Lake Reservoir (Moyle 2002).

In 1984, the spawning run out of Upper Klamath Lake was about 23,000 suckers; it declined to around 12,000 in 1985 (Matthews and Moseley 1990, Scoppettone and Vinyard 1991). In 1986, 95% of the individuals in Upper Klamath Lake were 19-30 years old; there had been little successful recruitment over the past 15 years (Scoppettone and Vinyard 1991).

Angler catch in the Williamson and Sprague rivers fell from more than 10,000 in 1968 to only 630 in 1985 (see Scoppettone and Vinyard 1991, Martin and Saiki 1999). USFWS (1990) categorized the status as "declining."

The population in Upper Klamath Lake declined substantially in a series of die-offs after the species was federally listed in 1988 (USFWS 2007).

By the late 1990s, as a result of die-offs in the mid-1990s, the number of adult fish in Upper Klamath Lake was 80 to 90 percent lower than observed prior to the mid-1990s; some increase in the spawning population was observed in the late 1990s, but the population is still at a relatively low level (about 40% of the 1995 level) (USFWS 2007). Presently, based on catch-per-unit-effort data, it appears that while the number of fish in the spawning population is still much lower than in the early 1990s, the breeding population numbers have at least been relatively stable since the late 1990s (USFWS 2007). Recruitment could increase in 5-10 years if survival is good among the large number of juveniles observed in 2006 (USFWS 2007).

Population growth in the lakeshore spawning population in Upper Klamath Lake occurred the late 1990s and 2000, and the lakeshore spawning population has been stable since then (Janney and Shively 2007). However, if recent survival rates persist, the current group of lakeshore spawners may be substantially reduced within the next few years, and unless there is improved recruitment during that period, the population will be at increased risk of extirpation (USFWS 2007).

Limited available data for Clear Lake suggest that there have been declines in the numbers of large adult suckers since 2000 (Barry et al. 2007).

While now apparently relatively stable, the overall population has declined substantially over the past three generations (generation length is probably 10 years or more).

Habitat includes deep-water lakes and impoundments, and swift water and deep pools of small to medium rivers. Suckers can be found throughout the reservoirs they inhabit, but they appear to prefer shorelines with emergent vegetation that can provide cover from predators and invertebrate food (Moyle 2002). Suckers move from lakes into tributary streams to spawn in riffles or runs with gravel or cobble substrate, moderate flows, and depths of 21-128 cm (USFWS 2007). Spawning also occurs along shore of Upper Klamath Lake (e.g., at spring inflows). Juveniles move downstream into lakes soon after hatching. Larval suckers prefer shallow, nearshore, and emergent vegetated habitat in both the lakes and rivers (NRC 2004). See USFWS (1988, 1993).

Current status is due primarily to: sucker mortality and habitat changes that resulted from the draining of the Tule Lake and Lower Klamath "basins" in the 1920s; adverse water quality, deriving in part from excessive nutrient inputs from agricultural sources, and causing algal blooms that in turn have resulted in massive sucker mortality; low water levels in Upper Klamath Lake caused by water removal for irrigation, hydroelectric generation, wildlife refuges, and instream flows for downstream fish populations (Kann and Walker 1999); diking and draining of wetlands bordering lakes (wetlands served as fish nursery habitat and probably buffered lakes from agricultural pollutants); and loss of spawning habitat due to damming of rivers (e.g., Chiloquin Dam constructed in 1928 on the Sprague River, Oregon, cut off access to 95% of historical spawning habitat for the Upper Klamath Lake population and precluded accumulation of suitable spawning gravels below the dam) (USFWS 1988, 1993, 2007; Scoppettone and Vinyard 1991; Perkins et al. 2000; Moyle 2002). Exotic fishes such as fathead minnow are abundant in some areas, but their effects on Lost River suckers are poorly known. The sport fishery in the 1960s and 1970s may have contributed to the decline (fishing for this species is now prohibited).

USFWS (2007) assessed current threats as follows (abbreviated):

The rate of habitat change has slowed markedly, but only a small fraction of the original habitat remains, and much of the remaining habitat is in a degraded condition. Restoration efforts are beginning to reverse the trend, but will probably require many years to produce a substantially increased and stable habitat base for the Lost River sucker.

Averse water quality is the most critical threat, and substantial improvement is not expected in the near future. Within the foreseeable future, there is a high probability of multiple mortality events that would greatly reduce population sizes. It is possible that infrequent recruitment would be unable to offset declines from such die-offs. However, though previous mortality events in Upper Klamath Lake resulted in substantial population losses, the sucker population was not extirpated and now again shows evidence of improvement. Thus, recruitment, although low, has enabled the Upper Klamath Lake population to survive, despite the impact of multiple mortality events.

Drought is a threat because of its potential to cut off spawning habitat, reduce rearing habitat, and increase disease, parasitism, and predation. However, historically the species has endured periods of prolonged drought and persisted, indicating that drought is not a major threat.

Fish entrainment in water diversions and restricted passage are threats. Entrainment at Link River Dam and associated hydropower diversions likely poses a risk to the sucker. The threat there could be reduced if the hydropower diversions were screened or eliminated, and if discharges at the dam could be modified to reduce entrainment. Passage to spawning habitat in the Sprague River is still impeded by Chiloquin Dam, but that structure is planned for removal in the near future. Elsewhere in the upper basin, some entrainment of suckers is occurring, but mostly larvae are entrained, and USFWS does do not consider this a substantial threat at the population level.

Overutilization for commercial, recreational, scientific, or educational purposes is not now regarded as a threat.

Disease, parasites, and predation/competition by exotic fishes pose some risk, although the degree to which they affect the species is not quantified. Disease and parasites alone may not pose a significant risk, but paired with the impacts of adverse water quality, they can substantially affect sucker survival.

Application of existing Endangered Species Act authorities, especially section 7, is probably maintaining existing sucker habitats and leading to reductions in mortality and improvements in habitat. However, given the continued vulnerability of the species to existing seasonal habitat conditions, these regulations have not been sufficient to substantially reduce the primary threat to the species.

Hybridization occurs among sucker species in the Klamath Basin, but it is not now regarded as a significant threat.

Additionally, Chiloquin Dam, a major impediment to upstream migration, is planned for removal in 2008. Reconnection of the Williamson River Delta (over 4,000 acres) by 2010 will likely provide significant habitat.

USFWS (2007) noted that high rates of participation in federal and state conservation programs by ranchers and farmers in the Sprague and Wood river valleys suggests that essential elements of habitat recovery on private land (i.e., voluntary participation and funding) are now in place. This should make it more efficient to conduct restoration in the future. Furthermore, the USFWS and its partners are committed to developing and implementing a rigorous monitoring program to evaluate the effectiveness of recovery actions and to providing a feedback loop for adaptive-management. These efforts, if successful and sustained, should help recover the Lost River Sucker. See USFWS (2007) for additional information on conservation activities that should benefit the Lost River Sucker.